The high-definition multimedia interface (HDMI) is a popular interface for transmitting high-speed baseband digital video and associated audio signals for presentation on an HDMI-capable device. Recently, high dynamic range (HDR) video display devices have become available, and video sources, such as digital versatile disc (DVD) players, television broadcasts, and on-line streaming services, now provide HDR content. HDR displays that receive HDR content provide higher brightness levels and may also provide darker black levels and improved color rendering as compared to standard dynamic range (SDR). SDR video refers to a dynamic range of between zero and 300 nits (cd/m2). Recently, display devices having dynamic ranges up to 10000 nits or greater have become available. These display devices are referred to as HDR displays. In order to accommodate these HDR displays and the corresponding HDR sources, video interfaces, including HDMI, have been adapted to transport both pixel data and SDR or HDR metadata over the interface.
Metadata for SDR video data is sent over the HDMI interface using auxiliary video information (AVI) information frames (InfoFrames). Currently, there are two types of HDR metadata, static HDR (S-HDR) metadata which is sent using DRange and Mastering (DRAM) InfoFrames, and dynamic HDR metadata which is sent using HDR Dynamic Metadata Extended (HDR DME) InfoFrames. S-HDR metadata is applied to an entire program while dynamic HDR metadata may change more frequently, typically over a sequence of several frames but could change frame to frame. The metadata in the DRAM InfoFrames and HDR DME InfoFrames augments the metadata in the AVI InfoFrames.
A source processing an HDR signal may be coupled to a sink (e.g., display) configured to display only SDR video or SDR video and one or both of S-HDR video or dynamic HDR video. When the sink does not support dynamic HDR, the source may convert the dynamic HDR video data to S-HDR video data or SDR video data before sending the video data to the sink. When the sink does not support S-HDR video or dynamic HDR video, the source may convert both S-HDR video data and dynamic HDR video data to SDR video data before sending the video data to the sink. A sink that is capable of displaying dynamic HDR video receives the video data over the HDMI interface using the HDR DME InfoFrame in a frame-synchronous manner so that the metadata is applied to the frame occurring immediately after the metadata is received.
To implement the frame-synchronous switching of the dynamic HDR metadata carried in the HDR DME InfoFrame, HDMI 2.1 defines a frame accurate packet area (FAPA) in the vertical blanking area of the video signal and specifies that HDR DME InfoFrames are to be sent during the FAPA period. HDMI 2.1 also specifies that AVI InfoFrames and DRAM InfoFrames are to be sent in a frame-synchronous manner, but HDMI 2.1 does not require that these InfoFrames be sent during any particular period within a video frame. Therefore, considering the timing requirements specified for transmission of InfoFrames, the timing of the HDR DME InfoFrame, is precisely specified to be transmitted during the FAPA period. The AVI InfoFrame and the DRAM InfoFrame are required to be frame-synchronous, but a specific time period for transmission is not specified.